Where I live on the eastern coast of the island of Newfoundland, summer usually starts closing down around the first week of August, and this year it's exactly on cue. For the past few weeks we've had off-and-on temperatures ranging between 20°C and 28°C (68°F - 72°F). Before that the average temperature was well below 15°C (59°F). My bees were more ore less in suspended animation for most of the spring and "summer." During the brief hot spell, the bees kick into high gear and make up for lost time in a hurry. But the warm weather didn't last long. I hope we get another heat wave.
Because nucs aren't available here until mid- or late-July, building a nuc into a full 20-frame colony before winter, especially if the nucs aren't ready until the end of July (the case for most people this year), we're fighting against the instincts of the bees. May to July, they want to build comb, even on crappy plastic foundation. But come August, the bees shift into hording mode and are less keen to build comb (especially once the nights get cold, which is happening now). I have to pull out every trick in the book to get my bees to build comb at times. Lots of inserting empty frames between drawn comb. Spiking syrup with anise to make the syrup more attractive. It can be a challenge for people who don't have a large number of hives to borrow resources from.
Seeing how the temperatures are already taking a dip, I've decided to go with the black paint, at least on the bottom deeps. My hives don't get full sunshine all day, so the extra solar heat from the black paint should help. If they were in full sunlight, they might overheat, but they're not, so I'm going for it. I don't see it as a problem during the odd day when the temperatures goes around 30°C (87°F), which probably won't happen again this year anyway.
I'm also going to keep them wrapped for a long as possible in the spring, instead of unwrapping after the first warm spell.
Thanks for the response, Jeff.